Process for the catalytic dehydrogenation of hydrocarbons



Patented Aug. 19, 1947 PROCESS THE CATALYTIC DEHYDRO- GENATION FHYDROCARBONS Robert L. Parker, Jr., Los Angeles, and Hal C. Huffman,Long Beach, Calif., assignors to Union Oil Company of California, LosAngeles, Calif., a corporation of California No Drawing. ApplicationDecember 21, 1948,

. Serial No. 515,122

11 Claims. (Cl. 260-680) This invention relates to the catalyticconversion of hydrocarbons and particularly to the dehydrogenationof'normally gaseous hydrocarbons in the presence of a novel catalyst.

It is known that when hydrocarbons are sub- .iected to elevatedtemperatures in the presence of catalysts, they may be converted orchanged in form. Well known conversion processes for example includecracking, reforming, and the like, as well as dehydrogenation and thelike. The type of conversion which occurs depends not only on thereaction conditions, but on the type of catalyst employed. Somecatalysts appear to affect predominantly the carbon to carbon bonds ofthe hydrocarbon, while others afl'ect predominantly the carbon tohydrogen bonds. It is clear that a catalyst of the former type shouldpreferentially promote cracking reactions, while a catalyst of thelatter type should preferentially promote dehydrogenation reactions, andthis has been observed to be true in a general way. 'Silica, forexample, appears to affect carbon to carbon bonds to a much greaterextent than does alumina, and consequently in making dehydrogenationcata- 2 tivity of the catalyst is enhanced, its heat stability isincreased, and its effective life is lengthened. The resulting catalystis particularly effective for the dehydrogenation of butanes to butenesand butenesto'butadiene. This type of dehydrogenation is of greatimportance at the present time because of the extensive use of butenesin alkylalysts, although alumina is frequently employed in 26substantial proportions as a carrier, silica is generally avoided.

It has now been discovered that the presence of a small proportion ofsilica in dehydrogenation catalysts, contrary to the indications of theprior art, is highly desirable, particularly with regard to increasingthe stability of the catalyst toward heat, and preserving its activityover a longer useful life. This desirable effect of silica isparticularly evident in the case of dehydrogenation of normally gaseoushydrocarbons, in which process the optimum proportion of silica in thecatalyst is about 1% by weight.

It is an object of this invention therefore, to provide an efllcientdehydrogenation process, whereby acyclic hydrocarbons having 2 to 5carbon atoms may be catalytically treated to increase their degree ofunsaturation; for example, butanes may be converted to butenes andbutadiene, butenes may be converted to butadiene, propane may beconverted to propene, and pentanes may be converted to pentenes,isoprene, etc. It is a further object to provide a novel andexceptionally useful catalyst for this process. Other objects willbecome apparent.

We have discovered that by incorporating a small amount of silica suchas about 1%, in a catalyst consisting predominantly of an alumina gelcarrier impregnated with minor proportions of chromia and beryllia, thedehydrogenating action processes for the production of aviationgasoline, and the use of both butenes and butadiene in the preparationof synthetic rubber and plastics.

As a specific example of our invention, a carrier consisting of analumina gel containing 0.9% silica was prepared by precipitation of thehydrous oxides from aqueous solutions of soluble salts of aluminum andsilicon, and this carrier was ignited in air at about 500 C. for about 2hours to convert it into a hard highly adsorptive gel. This product,screened to 8 to 20 mesh size, was then impregnated with solutions ofberyllium and chromium salts as follows: to 900 grams of the ignitedcarrier was added 3'79 grams of beryllium nitrate Be(NOa) 2.3H2Odissolved in 800 ml. of distilled water. The mixture was heated todryness with constant agitation, and the resulting material was driedfor 16 hours at about 250 C. followed by a 2 hour ignition at 500 C.

To this beryllia,-impregnated product was added a solution of 84 gramsof ammonium dichromate (NR4) 2C12O'1 dissolved in 800 ml. of distilledwater, and this mixture was heated to dryness with agitation, dried andignited as above, to obtain a finished catalyst containing about 5% byweight of beryllia, 5% of chromia, 0.8% of silica, and the remainderalumina.

The above catalyst was employed to dehydrogenate butane in the followingoperation: gaseous n-butane was preheated and passed at a rate of 5liters per hours through 5 ml. of the above catalyst in a reactionchamber at a temperature of about 565 C. (1050 F.) and substantiallyatmospheric pressure. This feed rate corresponds to a space velocity(volumes of feed gas, measured at 0 C. and 760 mm. pressure, per volumeof catalyst per hour) of 912. Under these conditions, the averageconversion of butane to butenes over a 2-hour reaction cycle was 34.4%(mol per cent) which is not far from the maximum theoretically possible(equilibrium) conversion at this temperature. The catalyst was thenregenerated by substituting a smaller flow of air for the n-butane flowfor a period of about 6 hours at about the same temperature. Butane wasthen substituted for the air flow for another 2-hour cycle similar tothe first cycle, and substantially the same conversion was obtained.

The heat stability, life, strength, and other characteristics of theabove catalyst are all reis subjected to a temperature of,850 C. in airare desirable for the dehydrogenation of ethane and propane, whilesomewhat lower temperatures are desirable for the dehydrogenation of thepentanes.

For the above dehydrogenation process, the preferred catalysts are ofthe type indicated above, 1. e., they should .consist of a gel type Ialumina carrier containing about 1% of silica,

In this test a sample of catalyst for a period of 6 hours. At th'end ofthis time its physical characteristics and catalytic activity are againdetermined, and any changes brought H about by the calcination arenoted. Usually, it

is found that catalysts supported on alumina lose their hardness, becomesoft and powdery, and lose most of their catalytic activity. This istrue ,.to a limited extent even of the above catalyst when the silica isomitted from its composition, With the silica incorporated however, theabove catalyst upon calcination at 850 C. retained substantiallyentirely its original form and mechanical strength, and gave a 24%conversion of butanes to butenes when tested as above. The 850 C.calcination test has been found to be a fairly reliable index of thebehavior of dehydrogenation catalysts over extended periods of usage; i.e., a good retention of strength and activity upon calcination at.850 C.generally indicates that the catalyst will also have a good retention ofstrength and activity in use over an extended period of time. Theresults of the above test indicate that this catalyst will preserve itsstrength and excellent activity through many hundreds of cycles of useand regeneration as described above.

The explanation for the remarkable effect of the silica on the catalystas described above is not known. It is only known that thesilicapromoted catalysts of the type described above have tremendoussurface area, larger than that of any other dehydrogenation catalysts ofsimilar type; and it also appears that the presence of the silica withthe alumina prevents or at least retards the conversion of the aluminato an inactive form.

The above catalyst is also very effective for' 100 to 500 mm. ofmercury. These low effective pressures may be attained either byoperating under vacuum at these total pressures, or by employing totalpressures as high as 2 or even 5 atmospheres, and having a diluent orinert gas such as nitrogen, methane and the like, present in suchproportions as to lower the effective pressure (1. e., the partialpressure of the hydrocarbons being converted) to a value within thedesired range. When butane is being dehydrogenated to butadiene, longercontact times, i. e., lower space velocities, such as about 300 or lessmay be used, while in the dehyrodrogenation of butenes, higher spacevelocities, such as 3000 or more may be used. In general the mostsuitable temperatures for butane and butene dehydrogenation are betweenabout 550 C. and 650 C., with higher space velocities b'eing employed atthe higher temperatures.

Other normally gaseous acyclic hydrocarbons having 2 to 5 carbon atomsmay also be dehydrogenated preferably under the conditions given above,although somewhat higher temperatures impregnated with solutions ofchromium and beryllium and ignited so as to obtain a finished catalystscontaining about 1% to 15% of chromia and about 1% to 15% of beryllia,by weight. For the'purposes of this invention, beryllia concentrationsof 1% to 5% are preferred. Although silica concentrations of about 1%are preferred, the silica has a pronounced beneficial effect even whenpresent in 0.5% or lower concentrations, and up to about 5%, and even insome instances as high as 15%.

The beneficial effects of small amounts of silica are not entirelylimited to the above catalysts nor to the above dehydrogenation process,however. It has been found, for example, that catalysts of the abovetype are excellent for all sorts of hydrocarbon conversion processessuch as cracking of gas oils and the like; isomerization of parafiins,olefins, and naphthenes; reforming, aromatizaton and hydroforming ofgasolines and naphthas; and like processes which are carried out attemperatures between about 400 C. and 900 C. in the presence or absenceof hydrogen. In hydroforming operations for example, which arepreferably carried out on liquid hydrocarbons such a petroleum naphthas,at temperatures between about 400 C. and 600 C. and pressures of 10 ormore atmospheres, in the presence of about 2000 to 10,000 cubic feet ofhydrogen per barrel of feed, the above catalysts are excellent,especially when the silica content is about 5%, or lies between about 1%and 10%. For catalytic cracking of gas oils, which is generally carriedout at temperatures between 450 C. and 550 0., similar catalystscontaining up to about 15% silica are preferred.

The alumina in the above catalysts is preferably the gel type, and maybe prepared by precipitation with ammonia of an aluminum chloride,nitrate, or sulfate solution, with thorough washing of the precipitateto remove soluble salts, or by any other suitable method for obtaining agelatinous alumina carrier. The silica is preferably coprecipitated withthe alumina from a silicon tetrachloride solution or other' i solution,but may be separately precipitated and adsorbed on the hydrousgelatinous alumina: .I 'he carrier of alumina-silica is dried andignited at about 500 C. to 600 C. to activate it and increase itsadsorptive power. It may be ground and pelleted, or extruded, or merelybroken into granules of suitable size, either before or after igniting.Commercial activated alumina may also be used, especially if it is thegel type. Crystalline, corundum, or alpha alumina, however, is noteffective in our catalysts.

In incorporating the chromium and beryllium into the above carriers, theimpregnation procedure as described above or merely dipping the ignitedcarrier in the solution of the chromium or beryllium salt are preferredmethods, but the chromium or beryllium hydroxides may also becoprecipitated with the alumina and silica, as by addition of ammonia tothe solutions of the nitrates or chlorides. If coprecipitated,

the product is dried, pelleted, etc. as described for the carrier.

It has been found that catalysts in which the other metals of group VI Bsuch as tungsten,

presence of about 0.5 to 15%, preferably about 1% to. 5% of silicaincorporated as above, improves any catalyst consisting of an activealumina (this term does not include the crystalline, corundum, or alphaaluminas mentioned above but does include gel and granular activatedaluminas) in combination with an oxide or sulfide of a metal of thetransition series, which term includes metals of group VI 3 as describedabove and metals of the groups having atomic numbers between 21 and 30or between 39 and 48. These latter groups constitute the first andsecond groups of the so-called transitional elements, in the structureof which the differentiating electron is in the second from theoutermost shell. This classification is the one set out by Luder in Animproved periodic table, Journal of Chemical Education, vol. 16, pages393 and 394 (August 1939), as an elaboration of earlier periodic tablesformulated by Ebel and by Bohr. The first transitional group includesscandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel,copper and zinc, and the second transitional group includes yttrium,zirconium, columbium, molybdenum, masurium, rubidium, rhodium,palladium, silver and cadmium. Of these active metals those of the firsttransitional group are preferred. The oxides or sulfides of these activemetals may be mixed, 1. e. deposited on the silica-alumina in the formof mixtures of oxides or sulfides or of compounds including 2 or moremetals, such as cobalt molybdate, cobalt thiomolybdate, copper vanadate,nickel chromite, and the like; It is preferable that such catalystscontain a minor proportion of beryllia also, such as about 1% to 15% asindicated above. The beryllia does not appear to have a catalytic effectby itself, such as is the case with the above active metal oxides, butit appears to promote and increase the catalytic effect of the activemetal oxides. This effect may or may not be analogous to the effect ofthe silica on the active alumina.

It has also been found that the desirable effects, of silica on theabove catalysts for hydrocarbon conversion, are also imparted byzirconia, and even by titania, although the silica is preferred.Silicon, titanium, and zirconium are all elements of group IV of theperiodic system. The zirconia and titania may be employed in about thesame amounts as the silica, i. e. about 0.5% to 15%, and are alsopreferably incorporated in the alumina by coprecipitation.

It is within the scope of this invention therefore to provide a processfor the conversion of hydrocarbons and a catalyst therefore whichcomprises an active alumina containing small amounts of silica andcompound of an active metal, and preferably also a compound ofberyllium.

Modifications of this invention which would occur to one skilled in theart are to be considered within the scope of the invention as defined inthe following claims:

We claim: 1. A process for the catalytic dehydrogenatio of hydrocarbonswhich comprises subjecting said hydrocarbons to an elevated temperaturein the presence of a catalyst comprising an activated alumina containingabout 0.5% to about 15% of an oxide of an element selected from a classconsisting of silicon, titanium, and zirconium, about 1% to about 15% ofberyllia and a minor proportion of an oxide of a metal of group VI B.

2. A process according to claim 1 in which the metal of group VI B ischromium.

3. A process for the catalytic dehydrogenation of hydrocarbons whichcomprises subjecting said hydrocarbons to an elevated temperature in thepresence of a catalyst comprising an activated alumina containingabout'll.5% to about 15% of silica, about 1% to about 15% of berylliaand a 4. A process according to claim 3 in which the metal of group VI Bis chromium.

5. A process for the-dehydrogenation of nor mally gaseous hydrocarbonswhich comprises subjecting said hydrocarbons to an elevated temperaturein the presence of a catalyst comprising an active alumina containingabout 1% of silica, about 1% to about 15% of beryllia, and a minorproportion of chromia.

6. A process for the production of butadiene which comprises subjectingbutenes to a temperature between about 550 C. and 650 C. in the presenceof a catalyst consisting of about 1% silica, 5% beryllia, 5% chromia and89% active alumina, said catalyst being prepared by a process involvingprecipitating a hydrous oxide gel of alumina and silica, drying andigniting said gel, impregnating it with compounds of beryllium andchromium and drying and igniting the product.

7. A process according to claim 1 in which the catalyst also contains anoxide of a different polyvalent metal selected from the class consistingof cobalt and nickel, in an amount approximately equimolal to the groupVI B metal oxide.

8. A process for the catalytic dehydrogenation of normally liquidnon-aromatic hydrocarbons which comprises subjecting said hydrocarbonsto an elevated temperature in the presence of hydrogen and a catalystcomprising an activated alumina containing about 0.5% to about 15% of anoxide of an element selected from the class consisting of silicon,titanium and zirconium, about 1% to 15% of beryllia, and a minorproportion of an oxide of a metal of group VI B.

'9. A process for the catalytic dehydrogenation of normally liquidnon-aromatic hydrocarbons which comprises subjecting said hydrocarbonsto an elevated temperature in the presence of hydrogen and a catalystcomprising an active alumina containing about 0.5% to about 15% ofsilica, about 1% to about 15% of beryllia, and a minor proportion of anoxide of a metal of group VI B.

10. A process for the catalytic dehydrogenation of hydrocarbons whichcomprises subjectabout 15% of an oxide of an element selected from theclass consisting of silicon, titanium and zirconium, about 1% to 15% ofberyllia and a I minor proportion of molybdena.

11. A process according to claim 10 in which the catalyst also containscobalt oxide in an Number Name Date amount approximately equlmolal t tD1 22 9 90 Weiss July 30 1940 lybdem- 1,782,857 Miller et a1. Nov. 25,1930 ROBERT PARKER- 2,134,234 Groil et al. (A) Dec. 19, 1939 HALHUFFMAN- 5 2,194,235 Groll et :91. (B) Dec. 19, 1939 2,172,535 Grosse eta] Sept. 12, 1939 REFERENCES CITED 2,354,392 Thacker 1 Aug. 1, 1944 Thefollowing references'are of record in the 2,346,657 Bloch et a]. Apr.18, 1944 file of this patent: 10 2,370,798 Kearby Mar. 6, 1945 UNITEDSTATES PATENTS 2,371,087 Webb 8!; a1. Mar. 6, 1945 OTHER REFERENCESNumber Name Date 2,325,398 Hearne et a1. July 27, 1943 h p i ti nary ofApplied Ch y, 2,330,804 Atkinson Oct. 5, 1943 (v01. 1) (1921). (Copy inDivision 31.)

2,325,911 Huffman Aug. ,3, 1943 15

